Growing an α-helical peptide from a substrate coated with a metallic film is known. An exemplary metallic film is made of gold, and the α-helical peptide is attached to the metallic film by a surface anchor. The anchor functions by chemically bonding with both the peptide and the film surface, thereby securing one to the other.
Prior-art anchors ordinarily bond to a metallic-film surface via a single sulfur-metal bond. In other words, prior-art anchors ordinarily have a single sulfur functionality that is reactive with a metallic-film surface. The deficiency of such anchors is that their resultant surface orientation is often uncontrollable and unpredictable. For example, their positioning is either substantially vertical or substantially parallel to the metallic-film surface. And that, in turn, directly impacts the, spatial orientation of an attached α-helical peptide. So if an anchor's spatial orientation is substantially parallel to a film surface, the attached α-helical peptide is also positioned substantially parallel to the film surface. Uncontrollable surface orientation is problematic because an α-helical peptide functions best as an optical switch when it is substantially vertical. The anchor's spatial orientation is therefore key.
In addressing the need for sulfur-based surface anchors having predictable surface orientation, the prior art teaches using a trithiaadamantane anchor to grow an α-helical peptide. Trithiaadamantane has a three-dimensional tripodal structure that provides more predictable surface orientation compared to single-sulfur anchors. Trithiaadamantane anchors form three sulfur-metal bonds with a metal surface, and that causes the compound to assemble in an upright vertical position. The anchor's upright surface orientation causes the α-helical peptide to likewise have a vertical spatial orientation, and that is preferred.
Prior-art trithiaadamantane anchors have previously been manufactured only by using the specific chemical intermediate- ethyl 2,4,9-trithiaadamantane-7-carboxylate. The prior art fails to provide useful alternate intermediates. A significant drawback to any method that employs ethyl-2,4,9-trithiaadamantane-7-carboxylate is that ethyl-2,4,9-trithiaadamantane-7-carboxylate can only be produced at the relatively low yield of about 10-25%.
So the art needs an alternate intermediate compound, one other than ethyl 2,4,9-trithiaadamantane-7-carboxylate, that can be used to produce trithiaadamantane anchors for growing α-helical peptides. There is also a need for an alternate intermediate compound that can be used in making trithiaadamantane anchors, wherein the alternate intermediate compound can be produced at a yield greater than the prior art's 10-25% yield for ethyl-2,4,9-trithiaadamantane-7-carboxylate. There is an additional need for methods directed to making trithiaadamantane anchors.